Exhaust gas emitted from internal combustion engines, such as gasoline engines or diesel engines, for automobiles and the like, contain harmful components, such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and the like.
Therefore, an internal combustion engine is typically provided with an exhaust gas purification device for decomposing and removing these harmful components, and most of the harmful components are rendered innocuous by an exhaust gas purification catalyst mounted in the exhaust gas purification device.
Known examples of the exhaust gas purification catalyst as described above include a NOx storage-reduction catalyst. The NOx storage-reduction catalyst is a catalyst which stores NOx contained in an exhaust gas in a lean atmosphere, and reduces the NOx to nitrogen (N2) in a stoichiometric atmosphere and a rich atmosphere, effectively utilizing the changes in the exhaust gas components in the lean, stoichiometric, and rich atmospheres.
However, a problem with respect to the purification of NOx in a lean atmosphere still remains, and various techniques have been examined and proposed.
Patent Document 1 discloses a metal-containing colloidal particle-supporting support in which metal-containing colloidal particles containing Nb and Rh are supported on a support material.
Patent Document 2 discloses an exhaust gas purification catalyst in which Rh is supported on a support, and the support is composed of an Nb oxide having an Allred-Rochow electronegativity in the range of 1.23 or more and less than 1.40.